The present invention relates to methods of reproducing coloured images and, in particular, to a method of reproducing a coloured image on a printable substrate.
More particularly the invention relates to an apparatus for reproducing a coloured image by scanning repeatedly the image by means of polychromatic photosensor means to generate signals indicative of polychromatic components of the elementary area, a dot printing device being controlled by said signals for printing corresponding coloured dots on a sheet.
Since these apparatuses require that the scan operation be repeated for each elementary chromatic component of the image, it is essential that the sheet be repeatedly brought in front of the printing device and be exactly repositioned at the beginning of each scanning operation.
There are known several kinds of image reproducing apparatuses of the above type. In one kind of apparatus both the photosensor means and the printing device are adapted to instantaneously scan one elementary line of the image and the sheet.
In a known apparatus of this kind the printable support is represented by a continuous web which is repeatedly reciprocated with respect to the printing device, whereby the web moving device is rather intricate and unreliable in operation.
Another kind of reproducing apparatus includes a transversely movable printing device for printing repeatedly a portion of the sheet. In a known apparatus of this kind, separate printing elements are provided for each colour, whereby the problem of exactly mutually positioning the sheet and the printing elements for the various colours is also faced.